In most municipal and many industrial water treatment processes, water must be subjected to precipitation and/or flocculation in a purification step in the separation process in order to obtain complete and effective removal of the pollutants from the water. Conventional chemical purification includes one or more flocculation tanks provided with stirrers or agitators followed by one or more sedimentation basins through which the water passes after addition of chemicals. A disadvantage of conventional chemical purification processes is the large area required for the flocculation tanks and sedimentation basins. A further disadvantage of conventional chemical purification techniques is the long time required for the water to remain in the flocculation tank as well as the sedimentation basin.
Furthermore, the use of flocculation tanks and sedimentation basins alone in the chemical purification step does not result in a high enough water purity for many applications. In such cases, a sand filter is added at the end of the purification step to increase the purity of the water being treated. The sand in such sand filters, however, must be cleaned by back-washing at frequent intervals and, in order to avoid shutting down the purification step, it is necessary to provide at least two sand filters, one of which is in use while the other is being backwashed.
It is an object of this invention to avoid the above-mentioned disadvantages of conventional purification steps.